We have studied a temperature-dependent gelation and retraction of Acanthamoeba extract in order to understand the mechanism of cell motility. We isolated several new proteins, four gelation factors and one retraction factor, from Acanthamoeba by procedures including DEAE-cellulose chromatography, ammonium sulfate fractionation, gel-filtration of Bio-Gel 1A 1.5m and hydroxylapatite chromatography. The former factors catalyze the gelation of actin and the latter induces the retraction of the actin-gel in the presence of ATP and Mg ions. Our work will focus on understanding the nature of interaction of these proteins with actin and the roles in motile functions of non-muscle cells.